Method of protection of date reproduction, and reproduction apparatus providing protection of data reproduction

ABSTRACT

In a reproduction apparatus, for reproducing an original signal conveyed as main data by a data medium such as a recording disk or broadcasting system, with medium protection data which are specific to the data medium being conveyed together with the main data, the apparatus includes a section for generating apparatus protection data which are specific to the reproduction apparatus, a section for combining the apparatus protection data with the medium protection data to define a protection level, and a section for applying the protection level to restrict reproduction of the original signal, with stepwise variations in restriction occurring in accordance with changes in protection level. The medium protection data may include information for specifying restricted reproduction of portions of the original signal, such as by producing degraded resolution within specified regions of specified frames of a video signal.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a data reproduction protectionmethod, and a data reproduction apparatus for implementing such aprotection method, whereby reproduction of a signal represented bydigital data such as a recorded digital video signal can be selectivelyrestricted.

[0003] 2. Description of the Prior Art

[0004] In the following, the term “data medium” is to be understood in avery general sense, as applying for example to broadcasting systemswhich transmit data such as video and/or audio data, in which case thereceived data may be the object of reproduction protection, and asapplying also to any type of recording medium such as recording disks ortapes, etc., in which case playback data derived from the recordingmedium may be the object of reproduction protection. The reproductionprotection may serve to selectively restrict viewing, hearing or copyingof the data.

[0005] In the prior art, various types of reproduction protection methodhave been applied in fields such as CATV (cable television) andsatellite television broadcasting. One method is to execute scramblingprocessing of transmitted video and audio data, and to insert acopyright code into the data, for thereby dividing the data intoportions which can be freely reproduced and portions for which a feemust be paid in order to reproduce the data. When a program for whichpayment of a fee is necessary is received by a receiving apparatus, theprogram can be unscrambled and reproduced only if specified paymentconditions are satisified.

[0006] In the case of recorded media, one method of reproductionprotection which is applicable to the DAT (digital audio tape recorder)recording system is the SCMS (serial copy management system). With thatmethod, the playback DAT signal from a DAT playback apparatus has a mainID (identification) number which includes a copy inhibit code, whereby asingle [(copy enable—copy inhibit] sequence is ensured, so that a usercan only make a single copy of a pre-recorded digital audio tape.

[0007] However with such prior art methods of reproduction protectionthere are only two control possibilities, i.e. reproduction is madeeither possible or impossible. It has not been possible hitherto toprovide a gradually varying degree of restriction of reproduction of asignal conveyed by a data medium. Thus, such a reproduction protectionmethod can only be used for a single purpose, e.g. for management ofpayment fees, or for copyright protection. Moreover with such a priorart reproduction protection method, since the data which are to beprotected exist only in a transmitting medium or recording medium priorto being reproduced, it has not been possible to provide a varyingdegree of limitation of reproduction capability in accordance with somecondition of the reproduction apparatus. Thus in some cases, the degreeof protection may be excessively severe, or excessively lax, so that itis difficult to achieve an effective degree of protection. For example,certain types of scenes recorded on a video tape may be permitted to beviewed in a certain country, such as the U.S.A., but may not bepermissible in other countries. It would be thus advantageous to ensurethat when that video tape is played on a reproduction apparatus which issold to the public in such other countries, reproduction protection isautomatically applied such that the aforementioned scenes will not bereproduced, or will not be clearly reproduced. However in the prior art,such a feature has not been possible.

SUMMARY OF THE INVENTION

[0008] It is an objective of the present invention to overcome theproblems of the prior art set out above, by providing a reproductionprotection method and apparatus whereby information specifying a degreeof restriction of reproduction of an original signal is conveyed (e.g.by a recording medium or signal transmission medium) together with dataexpressing the original signal, whereby information specifying a degreeof restriction of reproduction of the original signal are generated by areproduction apparatus which operates on the conveyed data, and wherebyinformation specifying a degree of restriction which is actually appliedto reproduction of the original signal is derived based on a combinationof the restriction information conveyed by the data medium and therestriction information generated by the reproduction apparatus.

[0009] More specifically, the invention provides a reproductionprotection method comprising:

[0010] attaching medium protection data to main data which are conveyedby a data medium, said main data representing an original signal;

[0011] supplying the main data and medium protection data, via the datamedium, to a reproduction apparatus;

[0012] generating apparatus protection data by the reproductionapparatus;

[0013] determining a protection level by combining the medium protectiondata and the apparatus protection data; and

[0014] controlling the reproduction apparatus to utilize the main datato reproduce the original signal in accordance with the protectionlevel.

[0015] It is a further objective of the invention to overcome the aboveproblems by providing a reproduction apparatus providing reproductionprotection, for operating on main data representing an original signaland medium protection data expressing a medium protection level, saidmain data and medium protection being conveyed by a data medium, theapparatus comprising:

[0016] means for detecting said medium protection data to obtain amedium protection signal expressing said medium protection level;

[0017] means for generating an apparatus protection signal expressing anapparatus protection level which has been assigned to said reproductionapparatus;

[0018] means responsive to said medium protection signal and apparatusprotection signal for determining a final protection level in accordancewith a combination of said medium protection level and apparatusprotection level;

[0019] means for executing reproduction of said original signal byutilizing said main data, including means for selectively restrictingsaid reproduction in accordance with said final protection level.

[0020] With such a method and apparatus for reproduction protection, theprotection level can determined in accordance with the medium protectiondata, and hence can be determined in accordance with the wishes of themanufacturer of the data medium, or of the copyright owner of the maindata. In addition, the protection level which is actually applied (i.e.the final protection level) is also determined in accordance with theapparatus protection data, which can be specified by the manufacturer orthe seller of the reproduction apparatus. As a result, when the maindata are to be reproduced (for example, during playback of a recordingdisk or tape), a graduated degree of limitation of reproduction isimplemented, with that degree of limitation being determined by thefinal protection level, i.e. being determined in accordance with acombination of the requirements of the data medium manufacturer or thecopyright owner of the main data and the requirements of themanufacturer or seller of the reproduction apparatus. In that way,considerable flexibility can be ensured in selectively restrictingreproduction of signals which are conveyed for example by recordingdisks or tapes or by broadcasting systems.

[0021] In particular, the invention enables such reproductionrestriction to be applied to specific frames or sequences of frames of avideo signal, or to specific regions within each of a sequence offrames.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a general system block diagram of a first embodiment ofthe invention, which is a CD player providing reproduction protection inaccordance with the present invention, for use in describing the basicprinciples of the invention;

[0023]FIG. 2 is a matrix diagram showing an example of how finalprotection levels are determined in a reproduction apparatus accordingto the present invention;

[0024]FIG. 3 shows specific examples of how medium protection levels canbe assigned;

[0025]FIG. 4 shows specific examples of how apparatus protection levelscan be assigned;

[0026]FIG. 5 is a general system block diagram of a second embodiment,which is a specific configuration for the apparatus of FIG. 1, whereinprotection control is applied to a data decompression section;

[0027]FIG. 6 shows examples of relationships between final protectionlevel values and video picture visibility grades, for three differentmethods of protection control of a video signal;

[0028]FIG. 7 is a general system block diagram of a third embodiment,which is a specific configuration for the apparatus of FIG. 1, whereinprotection control is applied to a video reproduction control section;

[0029]FIG. 8 is a conceptual diagram for describing how time-axisprotection and spatial-domain protection control can be applied to avideo signal with the present invention;

[0030]FIG. 9 is a diagram for describing how video, audio and protectiondata can be conveyed in a data stream in accordance with the MPEG1standards;

[0031]FIG. 10 is a block diagram of an example of the internalconfiguration of a video reproduction control section in the embodimentof FIG. 7;

[0032]FIG. 11 is a general system block diagram of a fourth embodiment,which is a specific configuration for the apparatus of FIG. 1, whereinprotection control is applied to a video reproduction control sectionand also to an audio reproduction control section;

[0033]FIG. 12 shows examples of relationships between final protectionlevel values and audio signal audibility grades, for three differentmethods of protection control;

[0034]FIG. 13 is a block diagram of an example of the internalconfiguration of an audio reproduction control section in the embodimentof FIG. 11;

[0035]FIG. 14 is a matrix diagram for illustrating how variable rangescan be defined for final protection level values, by a fifth embodimentof the invention;

[0036]FIG. 15 is a general system block diagram of the fifth embodiment,wherein a final protection level can be modified by operation of aswitch provided on the reproduction apparatus; and

[0037]FIG. 16 shows relationships between medium protection level valuesand settings of a modification switch in the embodiment of FIG. 15, foreach of respective values of the apparatus protection level.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0038] Embodiments of the invention will now be described, in which thedata medium is assumed to be a recording medium, specifically a CD(compact disk), having video and audio signal data recorded thereon. Inthe following, such data representing original signals which are to bereproduced from the data medium will be referred to in general as themain data, to distinguish these from protection data, which are alsoconveyed by the data medium as described hereinafter. It will further beassumed that the original video and audio signals have been encoded byhigh-efficiency compression encoding using the MPEG1 algorithm, prior torecording. The MPEG1 algorithm is described for example in“International Standards for Multimedia Encoding”, edited by Yasuda,published by the Maruzen company in Japan. FIG. 1 is a diagram fordescribing the general features of the reproduction protection methodand reproduction protection apparatus.

[0039] Protection Information Provided on Recording Medium

[0040] The concept of medium protection data will first be described,referring to FIG. 1, in which data recorded on a CD (compact disk) 1 areread out from the disk to obtain an input signal for a demultiplexer 10of a CD player 2, which is shown in block diagram form and which isconfigured to provide reproduction protection control in accordance withthe present invention. The CD 1 has video and audio signals recordedthereon as digital data (referred to in the following as the main data),using MPEG1 compression encoding. Protection data, which arepredetermined in accordance with the contents of the main data and willbe referred to as the medium protection data, are also recorded on theCD 1. The medium protection data consist of information to be used inselectively restricting reproduction of the main data, as describedhereinafter. The medium protection data can for example be recordedwithin the main code and sub-code header regions of the CD 1, or in theuser region of the compressed data. The medium protection data expressesa protection level, referred to as the medium protection level, whichcan for example take values which successively increase in five steps,from 1 to 5, as shown in FIG. 2 and described hereinafter. In that case,the medium protection data can express the medium protection level by 3bits. If separate medium protection levels are provided for the recordedvideo and audio data, then these can be expressed by two sets of 3 bits.The higher the number of the medium protection level, the greater is thedegree of protection (i.e. the greater becomes the degree of restrictionof reproduction of the recorded video or audio signal). The limitationof reproduction can for example by effected, in the case of video data,by operating on the playback data obtained from the CD1 such as toproduce an output video signal, from the apparatus of FIG. 1 which willresult in a mosaic pattern being produced within all or a specificregion of a resultant displayed picture, as described hereinafter.

[0041] The medium protection level which is expressed by the mediumprotection data is predetermined in accordance with the wishes of themanufacturer or seller of the data medium (CD 1), or of the owner of thecopyright for the main data. FIG. 3 shows two examples of mediumprotection data, each expressing 5 values of medium protection level. Inthe first example, limitation of reproduction is based upon the filmclassification system (i.e. movie ratings system) which is used in theU.S.A. In the case of a film which is rated “free”, no restriction onreproduction is imposed by the medium protection data. If the movie israted “PG” (i.e. parental guidance), then a moderate degree ofrestriction (protection level 1) is applied, and so on with increasingdegrees of restriction for the “R” and “X” ratings. In the secondexample, limitation of reproduction is based on the rights of thecopyright owner, providing successively increasing degrees ofrestriction of reproduction as the protection level increases from 1 to5.

[0042] The medium protection data is a combination of data forexpressing at least one medium protection level as described above, andprotection position information which specifies the position (within theencoded main data) at which the protection is to be applied. It is anessential feature of the present invention that the medium protectiondata can assign the medium protection level in units of frames of thevideo signal. That is to say, limitation of reproduction of individualframes can be controlled. In addition, limitation of reproduction of oneor more specific regions within a specific frame (or sequence ofspecific frames) can also be predetermined by the medium protectiondata. In that case, for example, a region formed of a number offixed-size blocks of pixels can be converted to a blank region, orfilled with a mosaic pattern, in the final display picture that isobtained from the output video signal from the apparatus of FIG. 1. Thatis to say, the protection position information can be used to specifynot only a specific frame, but also to specify one or more specificregions within a frame.

[0043] Alternatively, the protection position information can specify anidentical medium protection level for the entirety of each of asuccession of video signal frames, or specify an identical mediumprotection level for one or more specific regions within each of asuccession of frames.

[0044] The term “protection position information” is used here, since itmay not be necessary to record explicit data constituting the protectionposition information on the CD1. Instead, that information can beinherently constituted by the positions at which respective mediumprotection data are located within the stream of compressed encoded maindata that have been recorded on the CD 1. For example, the apparatus maybe configured such that if the encoded data for a video signal frame areimmediately preceded by a portion of medium protection data, then thatindicates that the medium protection data portion is to be applied tothat frame. If the medium protection data portion is to be applied toone or more regions within that frame, rather than the entire frame,then the medium protection data portion which immediately precedes thecompressed encoded frame in the recorded data can include at least twovalues for each of these regions, for specifying the respectivepositions of the regions. In that case, explicit protection positioninformation must be recorded as data on the CD 1, as part of the mediumprotection data.

[0045] Protection Information Generated by Reproduction Apparatus

[0046] With the method and apparatus of the present invention, areproduction apparatus can be configured to produce predeterminedprotection data which are specific to that reproduction apparatus. Forexample, the CD 1 in FIG. 1 is played by a reproduction apparatus 2which is provided with a presettable memory device which will be assumedto be a ROM (read-only memory) which generates apparatus protection dataexpressing a protection level referred to in the following as anapparatus protection level. The apparatus protection level is specifiedbeforehand by the manufacturer or the seller of the reproductionapparatus. In the same way as for the medium protection data describedabove, the apparatus protection level can take a plurality of values,corresponding to respectively different degrees of limitation ofreproduction of main data which are obtained from a data medium. It willbe assumed that the number of apparatus protection level values is 4,i.e. from 1 to 4, so that the apparatus protection data can be consistof two bits. The higher the apparatus protection level number, thegreater becomes the degree of protection, i.e. the greater becomes thedegree of reproduction limitation.

[0047] The contents of the apparatus protection data ROM cannot berewritten by the user. In the embodiment of FIG. 1, each time that powerto the apparatus is switched on, the apparatus protection data are readout from the ROM, and thereafter reproduction is executed in accordancewith a combination of the apparatus protection level specified by theapparatus protection data and the medium protection level which isspecified by the medium protection data.

[0048]FIG. 4 shows three examples of how the apparatus protection levelcan be assigned. In the first example, the apparatus protection level ispreset in accordance with the country in which the reproductionapparatus is to be used. If the reproduction apparatus is to be used inthe U.S.A. for example, then it is possible that the apparatusprotection level could be set to a low value such as 1. In the case of areproduction apparatus which is to be used in other parts of the world,such as Europe, Japan and Taiwan, which have varying degrees ofrestrictions on video software, the apparatus protection level could beset to higher values, as illustrated. In that way, video scenes whichare not permissible in one country can be automatically eliminated(partially or completely), e.g. by insertion of mosaic pattern regionsin the resultant display picture, by using the apparatus protectionlevel and medium protection level in combination as describedhereinafter.

[0049] With the second example in FIG. 4, the apparatus protection levelis predetermined in accordance with the type of person who is expectedto use the reproduction apparatus. If the reproduction apparatus is tobe used only by adults, for example, then the apparatus protection levelcan be set at a low value such as 1. If the reproduction apparatus willbe used by children, the apparatus protection level can be set to a highvalue such as 4. In that way, video scenes or audio content which areconsidered unsuitable for children can be partially or completelyrestricted from being reproduced.

[0050] With the third example in FIG. 4, the protection level that isset by the apparatus protection data is predetermined in accordance withthe applications for which the reproduction apparatus will be used. Forexample if the reproduction apparatus is to be sold to the public, thenthe apparatus protection level can be set to a value such as 1 or 2,whereas if the reproduction apparatus is intended to be used fordemonstration purposes in a shop, then the apparatus protection levelcan be set to a different value, i.e. 3 or 4, and the apparatus of FIG.1 controlled such that only certain scenes which should be of interestto possible customers of the shop will be displayed. In that way, theapparatus protection level can be set in accordance with the applicationobjectives of the reproduction apparatus.

[0051] The overall features of reproduction protection will now bedescribed, referring to FIG. 1. Firstly, data recorded on the CD 1 areread out, as an input signal to the demultiplexer 10. The recorded dataon the CD 1 consist of the compressed encoded main data (i.e. compressedencoded video and audio data) which are multiplexed with the mediumprotection data. The demultiplexer 10 separates the compressed encodedmain data from the medium protection data, and supplies the mediumprotection data to a medium protection signal detection section 11 whilesupplying the compressed encoded main data to a video decoder section15. As described hereinabove, the medium protection data may inherentlyspecify protection position information, or may include explicitprotection position information. The medium protection signal detectionsection 11 serves to detect the protection position information, andgenerates a corresponding protection position signal, which indicatesthose portions of the main data to which the medium protection dataapplies (e.g. specific video signal frames, and/or block regions withinspecific frames). The protection position signal is supplied to aprotection control signal generating section 14. The medium protectionsignal detection section 11 is further responsive to the mediumprotection data for generating a corresponding medium protection signal,which expresses the medium protection level and is supplied to a finalprotection level determining section 13.

[0052] The final protection level determining section 13 basicallyconsists of a matrix ROM in this embodiment, i.e. a ROM which stores apattern of relationships between respective combinations of mediumprotection levels and apparatus protection levels and resultant finalprotection levels. The operation of the matrix ROM will be describedreferring to the matrix diagram of FIG. 2, which shows an example of howthe contents of that ROM are read out in response to combinations ofmedium protection level and apparatus protection level values. There arefive possible values (designated as A to E respectively) for the finalprotection level, successively increasing in degree of reproductionlimitation in the sequence A, B, C, D, E. FIG. 2 shows an example ofvarious values of the final protection level which are determined byrespective combinations of values of the medium protection level andapparatus protection level, i.e. the values in the range A to E whichare located at respective intersections between rows and columns of thematrix in FIG. 2. Thus for example if the medium protection level is 4and the apparatus protection level is 2, then the final protection levelwill be B.

[0053] It is necessary to clearly distinguish between the ROM of theapparatus protection signal generating section 12 and the matrix ROM ofthe final protection level determining section 13. The contents of theROM of the apparatus protection signal generating section 12 can be setin accordance with the requirements for a particular reproductionapparatus, whereas the contents of the matrix ROM of the finalprotection level determining section 13 will in general be common to alarge number of reproduction apparatus units.

[0054] The final protection level determining section 13 generates anoutput signal, referred to as the final protection level signal, whichexpresses the final protection level that has been determined, andsupplies that signal to the protection control signal generating section14. In response to that signal, and the protection position signal, theprotection control signal generating section 14 generates a signalreferred to as the protection control signal, which is supplied tocontrol a section which will be referred to as the video decoder section15. For simplicity of description, only video signal reproduction willbe considered at this stage, and the video decoder section 15 should beunderstood as a section which converts the compressed encoded video data(main data) from the demultiplexer 10 to a standard (analog) videosignal. As the stream of compressed encoded main data flows into thevideo decoder section 15 from the demultiplexer 10, the protectioncontrol signal controls the video decoder section 15 such as to applyreproduction protection in accordance with the final protection levelvalues, at the respective positions within that data flow which arespecified by the protection position information. The video decodersection 15 thereby produces an output video signal which will result invideo pictures in which reproduction of the main (video) data is limitedin accordance with the final protection level values. As will beunderstood from the above, the final protection level values may changefrom frame to frame of the video signal, in accordance with changes inthe medium protection level.

[0055] A first example of limitation of reproduction in accordance withthe final protection level will be described, which is implemented bycontrolling the expansion and decoding of the main data by the videodecoder section 15. The example will be described referring to theembodiment of FIG. 5, in which the reproduction apparatus is again a CDplayback apparatus, designated by numeral 3. Only the operation withregard to the video data of the main data from the CD 1 will bedescribed. In FIG. 5, a specific configuration for the video decodersection 15 of FIG. 1 is shown, made up of a variable-length decodingsection 15 a, a dequantizer section 15 b, an inverse transform section15 c and a video reproduction control section 15 d, with the compressedencoded video data being supplied from the demultiplexer 10 to thevariable-length decoding section 15 a and with the final output (analog)video signal being produced from the video reproduction control section15 d. In this embodiment, the video data have been recorded on the CD 1after being subjected to compression by discrete cosine transformprocessing, and reproduction limitation is controlled by controlling theaccuracy of inverse DCT (discrete cosine transform) processing which iseffected by the inverse transform section 15 c. The protection controlsignal which is produced from a protection control signal generatingsection 14 a and supplied to control the inverse transform section 15 cis derived based on the medium protection data and apparatus protectiondata, in combination, as described above for section 14 in FIG. 1, i.e.the protection control signal applies control in accordance with thefinal protection level.

[0056] The demultiplexed compressed encoded video data read from the CD1 are subjected to variable-length decoding in the variable-lengthdecoding section 15 a, and then to dequantization in the dequantizersection 15 b. The resultant compressed data are then subjected toinverse DCT processing in the inverse transform section 15 c, with thetransform processing being selectively modified in accordance with theprotection control signal. The resultant decompressed data are thenprocessed in the video reproduction control section 15 d to obtain thefinal output video signal. The effect of reproduction limitationcontrolled by the protection control signal acting on the inversetransform section 15 c is to selectively produce a degree of blurring orformation of a mosaic pattern within the pictures which are displayedusing the final output video signal. Such a degree of blurring will bereferred to as the visibility grade. An example of the relationshipbetween the visibility grade and the final protection level values A toE (which are determined by the protection control signal generatingsection 14 a as described hereinabove, and are expressed by theprotection control signal) is shown in the leftmost column of FIG. 6. Ifthe protection level is A, i.e. minimum limitation of reproduction ofthe video data, then the protection control signal is set to a statewhereby it does not affect the operation of the inverse transformsection 15 c. If the protection level is B, then the protection controlsignal controls the inverse transform section 15 c such as to operate ona block size of 8×8 picture elements (i.e. the same block size which wasutilized in the original DCT processing), using the DC component valuefor each block, but using only two of the AC transform coefficients,with the values of all of the other transform coefficients beingforcibly set to zero. This will result in a substantial lowering ofresolution of a display picture that is produced based on the outputvideo signal. If the protection level is C, then the protection controlsignal controls the inverse transform section 15 c such as to operate ona block size of 8×8 picture elements of a video signal frame, using onlythe DC component for each block, (i.e. the DC component is the onlytransform coefficient used). In this case, since all of the pictureelements within an 8×8 picture element block will have identical videosignal values, this will result in a mosaic pattern being formed in thefinally obtained picture. If the protection level is D, then theprotection control signal controls the inverse transform section 15 csuch as to operate on a block size of 16×16 picture elements, using onlythe DC component values. This will again result in a mosaic patternbeing formed, in which the blocks of the pattern are of larger size thenfor the case of protection level C, i.e. a mosaic pattern of macroblocksis formed, thereby further degrading the degree of visibility of theresultant picture. If the protection level is E, then the video dataobtained from the inverse transform section 15 c are replaced bydifferent video data (produced from a source not shown in the drawing),which are produced from the video reproduction control section 15 d asthe final video signal, and which will produce a predetermined pictureor pictures. Such a predetermined picture might for example display awarning message concerning copyright protection.

[0057] With the MPEG1 algorithm, a block size of 8×8 picture elements isused in the DCT processing. The transformed block is expressed by a DCcomponent (i.e. DC coefficient) and a plurality of coefficients (the ACcoefficients) which represent signal level values at respectivelydifferent successively increasing frequencies. Thus if for example theinverse transform section 15 c is controlled such that only the DCcoefficient and the two lowest-frequency AC coefficients are used, inthe inverse DCT operation for each block, then a specific reduction inresolution of all (or a specific part) of the resultant display picturecan be achieved in a very simple manner.

[0058] Similarly if only the DC component for a block is used in theinverse DCT processing, with all of the AC coefficients set to zero,then all of the signal level values for the picture elements of a blockwill be set to an identical value, in the resultant video signalobtained from the inverse DCT operation. Hence, a mosaic pattern canvery easily be formed in the resultant picture that is obtained usingthe final output video signal. Moreover if, for each of respective 16×16element macroblocks (i.e. each consisting of four 8×8 picture elementblocks), only the DC coefficient for a specific one of the 8×8 elementblocks is used (for example, the DC coefficient for the upper leftmostone of the 8×8 element blocks) in the inverse DCT processing for all ofthe four 8×8 element blocks constituting the 16×16 element macroblock,with all of the AC coefficients set to zero, then a mosaic pattern willbe formed which is substantially coarser than the mosaic pattern whichis formed by using the 8×8 element blocks.

[0059] It can thus be understood that with the above embodiment of theinvention, applied to video data which have been subjected tohigh-efficiency compression encoding using a data transform operation,stepwise changes in a degree of restriction of reproduction of the videodata can easily accomplished by effecting stepwise changes in a degreeof resolution of a finally obtained picture, or in a portion of thatpicture, and that such stepwise changes in resolution can be easilycontrolled in accordance with the final protection level which has beenestablished based on the medium protection data and apparatus protectiondata. In particular, when such control is applied to the inverse DCTprocessing, it is possible to easily effect stepwise changes in thevisibility grade, i.e. in the picture resolution, through use of unitblocks of picture element values which are basic to the transformprocessing. Such a type of control of the visibility grade, operatingwithin each frame of the video signal, can be considered as applyingprotection in a (2-dimensional) spatial domain.

[0060] With a video data encoding method such as the DCT method, theoutput digital signal that is produced from the inverse DCT circuitconsists of sequential sets of data, each consisting of successivepicture element values for the respective picture elements of a unitblock (e.g. a block of 8×8 picture elements) of a video signal frame. Inorder to convert such a digital signal into a normal digital videosignal, it is necessary to first temporarily store the data producedfrom the inverse DCT circuit in a video memory (e.g. a frame memory),then to read out the video data in the correct sequence (i.e. assuccessive picture element values in successive picture scanning lineintervals). That operation is the basic function of the videoreproduction control section 15 d in FIG. 5. FIG. 7 shows anotherembodiment of the invention, in which control for reproductionprotection is applied to the video data which have been produced fromthe inverse transform section 15 c, i.e. in which control by theprotection control signal in accordance with the final protection levelis applied to a video reproduction control section which is configuredsuch as to respond appropriately to the protection control signal, andis designated as 15 d′. Apart from this feature, the configuration andoperation of this embodiment is identical to that of FIG. 5 describedabove. The video reproduction control section 15 d′ includes a framememory, into which output data from the inverse transform section 15 care temporarily written, and then read out in the appropriate sequenceas described above, to obtain the final output video signal.

[0061] In this embodiment, the degree of reproduction limitation iscontrolled by “thinning out” frames of the video data that are used toform the final output video signal, with the degree of “thinning out”being determined by the final protection level. That is illustrated bythe central column in FIG. 6, in which such a type of control isreferred to as time domain protection. In the example of FIG. 6, whenthe final protection level is A, then all of the frames of video datawhich are successively written into the frame memory of the videoreproduction control section 15 d′ are used to form the final outputvideo signal. If the final protection level is B, then the protectioncontrol signal from the protection control signal generating section 14b controls the video reproduction control section 15 d′ such that onlyone out of every 15 frames of video data supplied from the inversetransform section 15 c is used to form the final output video signal.Specifically, one out of every fifteen frames of video data from theinverse transform section 15 c is held stored in the frame memory of thevideo reproduction control section 15 d′ for fifteen successive frameperiods, and is repetitively read out during that time, to form thefinal output video signal. Thus a type sample-and-hold operation isperformed using the frame memory in the video reproduction controlsection 15 d′, whereby the finally obtained picture will change once inevery 0.5 seconds. If the final protection level is C, then the videoreproduction control section 15 d′ is controlled such that the contentsof the frame memory are updated only once in every 60 frame periods,i.e. the finally obtained picture will change only once in every 2seconds. If the final protection level is D, then only the video data ofcertain specific frames (or one specific frame) are written into theframe memory of the video reproduction control section 15 d′ and readout to obtain the final output video signal. In that way, for example,only a portion of the video data (e.g. a portion which is not subject tocopyright protection) will be displayed. If the protection level is E,then the video data for a predetermined picture are written into theframe memory of the video reproduction control section 15 d′ andrepetitively read out, to display only that predetermined picture, whichcan be for example a warning message concerning copyright protection.

[0062] Alternatively, control of the degree of reproduction limitationcan be performed by arranging that the protection control signal fromthe protection control signal generating section 14 b acts on the videoreproduction control section 15 d′ such as to vary (in accordance withthe final protection level) the number of gradations provided by eachvideo data sample, i.e. to vary the number of amplitude levels that canbe expressed by each sample. That can be performed by setting one ormore low-order bits of each data sample to a fixed value, e.g. 0. Forexample if the LSB is always set to 0, then the number of possiblegradations is reduced by half, and a corresponding lowering ofresolution of the finally obtained display picture is achieved. The bitsin each digital data sample which are not fixed in that way will bereferred to in the following as the effective bits of the sample. Suchgradation control based on the numbers of effective data bits isillustrated by the right-side column in FIG. 6. In that example, if thefinal protection level is A, then the protection control signal from theprotection control signal generating section 14 b has no effect on theoperation of the video reproduction control section 15 d′, so that eachvideo data sample used to form the output video signal has the standardnumber of effective bits, i.e. 8 bits. If the final protection level isB, then the protection control signal controls the video reproductioncontrol section 15 d′ such that the number of effective bits/sample ofthe output video signal is reduced to 4 (i.e. by rounding-off thelow-order 4 bits to zero). If the final protection level is C, then theprotection control signal controls the video reproduction controlsection 15 d′ such that the number of effective bits/sample is 2 (i.e.all except the two high-order bits are set to zero), so that the pictureresolution is further degraded. Similarly, if the final protection levelis D, then the video reproduction control section 15 d′ is controlledsuch that the number of effective bits is reduced to 1. If theprotection level is E, then the video data for a predetermined pictureare written into the frame memory of the video reproduction controlsection 15 d′ and repetitively read out as the final output videosignal, to display only that predetermined picture.

[0063] It would be equally possible, as indicated by the broken-lineconnection from the protection control signal generating section 14 b tothe dequantizer section 15 b in FIG. 7, to arrange that the protectioncontrol signal from the protection control signal generating section 14b acts on the dequantizer section 15 b such as to vary (in accordancewith the final protection level) the number of effective bits of eachoutput datum from the dequantizer section 15 b. That will provide asimilar effect to that described above for the case in which control iseffected through the video reproduction control section 15 d′.

[0064] Another method which may be used to control the degree ofreproduction limitation is to apply the protection control signal fromthe protection control signal generating section 14 b such as to controlthe variable-length decoding section 15 a. In that case, the protectioncontrol signal is arranged to act on the variable-length decodingsection 15 a such that, as the protection level is increased from A toE, data having a long code length are set to zero, i.e. are ignored.This will result in a lowering of resolution in the final picture thatis obtained from the output video signal.

[0065] It should be noted that reproduction limitation control can beexecuted by a combination of control acting along the time axis andcontrol acting in a spatial domain (i.e. within individual frames). Thatpoint is illustrated conceptually in FIG. 8, in which successivevertical lines 20 represent sequential frames of the video signal thatis recorded on the CD 1. (For simplicity of description, it will beassumed that the final protection level is identical to the mediumprotection level). Together with each video signal frame data portion onthe CD 1, a medium protection data portion is recorded, which mayinclude position information specifying a region within the frame withinwhich display resolution is to be lowered, to a degree that is inaccordance with the final protection level. In this example there aretwo possible basic display conditions for each frame, i.e. non-displayor display (with one or more degraded resolution regions possibly beingformed). To achieve this, the medium protection data assigned to eachframe includes a 1-bit flag, whose 1 or 0 logic state designates eitherdisplay or non-display for the frame. If that flag bit indicates thatnone of the frame is to be displayed, the condition is indicated by a“x” symbol in FIG. 8, while if the flag bit indicates that the frame isto be completely or partially displayed, that condition is indicated bya “o” symbol in FIG. 8. In the example of FIG. 8, a “o” condition isspecified for each of the ten consecutive frames designated as F_(A),indicating that each frame is to be displayed. In addition, the mediumprotection data of each of these frames includes position informationfor a degraded resolution region. The resultant display picture isdesignated by numeral 21, containing a degraded resolution region 22,which is rectangular and is shown as a hatched-line region. The degradedresolution region 22 is formed by a plurality of 16×16 elementmacroblocks, and for each of the frames F_(A), the correspondingposition information in the medium protection data specifies twoaddresses of macroblocks (designated as 22 a and 22 b, located at theupper left-side and lower right-side corners of the mosaic region 22)within the frame, to thereby specify the position and size of arectangular region which is the degraded resolution region 22.

[0066] Similarly, a set of four successive frames F_(B) is each to bedisplayed, but with a degraded resolution region formed in the finaldisplay picture, as indicated by numeral 24. In this case the degradedresolution region is formed of two adjoining rectangular regions, sothat it is necessary for the position information in the mediumprotection data to specify the positions of two pairs of macroblockswithin the frame, i.e. the pair of addresses of macroblocks 24 a, 24 band the pair of addresses of macroblocks 24 c, 24 d in FIG. 8.

[0067] It can thus be understood that in this case, reproductionprotection is applied by a combination of control with respect to thetime axis, and control with respect to (2-dimensional) space within eachframe. It can be further understood that the invention enables extremelyprecise control of reproduction limitation, which is determined inaccordance with the final protection level.

[0068] With data transmission in accordance with the MPEG1 system (i.e.based on the ISO-11172-3 standards), data are transmitted as successivepacks of data, which are time-division multiplexed, as illustrated bythe data flow 40 shown in FIG. 9. Each pack is made up of a leadingportion such as the portion 41, which contains information including apack start code and a stream identifier which distinguishes the dataconveyed by that pack from that of other packs (e.g. to distinguishbetween video, audio or other data), and a main data portion such asportion 42. In this example each main portion consists of eithercompressed encoded video data such as portion 42, encoded audio datasuch as portion 43, or protection data such as portion 44. In thisexample it will assumed that protection of the form shown in FIG. 8 isapplied to the video data, so an individual protection data portion maybe assigned to each of a plurality of video signal frames, i.e. videodata frames can be conveyed by respective packs, each preceded by aprotection data pack. In that case, each protection data pack in theexample of FIG. 9 consists of a 3-bit portion which specifies the mediumprotection level, a 1-bit frame flag specifying whether or not the frameis to be displayed (as described above for FIG. 8), a portion whichspecifies the number of macroblock start/end address pairs (to beutilized when at least one degraded resolution region is to be formedwithin the frame, e.g. as for each of the frames F_(A) and F_(B) in FIG.8), followed by the pairs of macroblock start/end addresses (e.g. thepair of addresses of macroblocks 24 a, 24 b, then the pair of addressesof macroblocks 24 c, 24 d, for each of the frames F_(B) in the exampleof FIG. 8).

[0069]FIG. 10 shows a specific internal configuration for the videoreproduction control section 15 d′ of the embodiment of FIG. 7. In FIG.10, the output data from the inverse transform section 15 c are suppliedvia a line 50 to a gradation control section 51, which is controlled byone of two protection control signals that are generated from theprotection control signal generating section 14 b, and resultant outputdata from the gradation control section 51 are transferred through aswitch 52, which is controlled by the other one of the protectioncontrol signals. Data transferred through the switch 52 are written intoa frame memory 53, and are subsequently read out from the frame memory53 in the appropriate sequence to constitute successive frames of theoriginal video signal. The digital video signal thereby produced fromthe frame memory 53 is supplied to a digital/analog converter 54, toobtain an analog video signal as the final output signal.

[0070] So long as the switch 52 is held closed, the contents of theframe memory 53 will be completely updated once in each frame period ofthe video signal, so that data of a new frame will be sequentially readout from the frame memory 53. However if the switch 52 is held closedduring an integral number of frame intervals, then the most recentlystored contents of the frame memory 53 will be repetitively read outduring each of these frame intervals, i.e. the last frame will becontinuously outputted. It will thus be apparent that this circuit canimplement the time-axis protection operation described above onsuccessive frames, if the switch 52 is controlled in accordance with thestatus of the frame bit that is contained in the medium protection data.

[0071] The gradation control section 51 operates on each digital videosignal sample (in general, each 8-bit datum) that is supplied from theinverse transform section 15 c, to set the low-order bits of each samplein accordance with the final protection level. For example referring tothe right-side column in FIG. 6, if the final protection level is B,then the gradation control section 51 sets all of the four low-orderbits of each sample to a predetermined value, e.g. 0. If the protectionlevel is D, then all of the seven low-order bits of each sample are setto 0.

[0072] If reproduction restriction is to be applied within a videosignal frame, then the protection control signal generating section 14 bresponds to the protection position signal such as to apply theabove-mentioned protection control signal to the gradation controlsection 51 during one or more specific time intervals within thecorresponding frame interval, with each of these specific time intervalsbeing determined based on one of the macroblock start/end address pairswhich are shown in FIG. 9, described above. In that way, reproductionlimitation can be applied within specific regions of a frame, asillustrated in FIG. 8, i.e. the spatial-domain protection operationdescribed above can be applied.

[0073] It will be understood that in practical terms, each “startaddress” will define a time-axis position, within a frame period, of thedata sample corresponding to an uppermost left-side pixel of arectangular region within the frame, while the “end address” similarlydefines the position of a data sample corresponding to a lowermostright-side pixel of that region. Such time relationships can be readilyestablished by well-known techniques for operating on a digital videosignal, so that detailed description is omitted.

[0074] In the above embodiments, only reproduction protection of videodata has been described. FIG. 11 shows another embodiment of theinvention, in which reproduction protection of both audio and video datais applied. Only the points of difference between this embodiment andprevious embodiments will be described. A CD reproduction apparatus 5 ofthis embodiment differs from that of FIG. 7 by including circuits fordecoding and dequantizing an encoded digital audio signal that has beenrecorded on the CD 1, by an audio decoding section made up of avariable-length decoding section 16 a, a dequantizer section 16 b, asub-band combining section 16 c and an audio reproduction controlsection 16 d. The compressed encoded audio data are separated from thevideo and protection data contained in the input data stream, by thedemultiplexer 10, and are supplied as input data to the variable-lengthdecoding section 16 a, with an output audio signal being produced fromthe audio reproduction control section 16 d. This embodiment furtherdiffers from that of FIG. 7 in that the protection control signalgenerating section 14 c of this embodiment produces not only a firstprotection control signal which acts on either the video reproductioncontrol section 15 d′ or dequantizer section 15 b to apply video signalreproduction protection by varying the number of bits per datum, asdescribed hereinabove for the protection control signal of theembodiment of FIG. 7, but also a second protection control signal whichacts on the audio reproduction control section 16 d or dequantizersection 16 b to apply audio signal reproduction protection, as describedin the following. For simplicity of description, it will be assumed thatthe second protection control signal is produced in accordance with thefinal protection level that is derived for reproduction protection ofthe the video data, as described hereinabove. However in general,separate medium protection levels and separate apparatus protectionlevels would be specified for the video and audio data, i.e. to obtainseparate final protection levels for video and audio data.

[0075]FIG. 12 is a table illustrating three possible methods of applyingaudio signal reproduction protection with the embodiment of FIG. 11.With each of the three examples shown in FIG. 12, five differentaudibility grades can be selected for the output audio signal producedfrom the audio reproduction control section 16 d, in accordance with thefinal protection level, to effect audio signal reproduction protection.Firstly, the method illustrated by the leftmost column in FIG. 12 willbe described. In this case, audio signal reproduction protection isapplied by selectively restricting the bandwidth of the output audiosignal produced from the audio reproduction control section 16 d inaccordance with the final protection level. If MPEG1 audio signalcompression is used, then assuming a sampling frequency of 48 KHz, abandwidth of 24 KHz is available for the output audio signal. In thisexample, if the final protection level is A, then no bandwidthrestriction is applied, i.e. the audio bandwidth is 24 KHz. If the finalprotection level is B, then the audio signal bandwidth is restricted to18 KHz, if the protection level is C the bandwidth is restricted to 12KHz, if the protection level is D the bandwidth is restricted to 6 KHz,and if the protection level is E then no audio output signal isproduced.

[0076] Since MPEG1 audio compression utilizes sub-band encoding with 32bands, such bandwidth restrictions can be effected by causing the secondprotection control signal to act on the dequantizer section 16 b such asto set the inverse quantization values corresponding to certainhigh-frequency bands to zero. Thus, audio reproduction protection bybandwidth control can be easily implemented.

[0077] A second method of audio signal reproduction protection will bedescribed referring to the central column in FIG. 12. In this case,time-axis protection is applied, by “thinning-out” of audio signalsample values that are supplied from the sub-band combining section 16 cand used in the audio reproduction control section 16 d to obtain theoutput audio signal. In this example, if the final protection level isA, then all of the audio sample values are used in deriving the outputaudio signal. If the final protection level is B, then one in every twosamples is held for two consecutive sample periods, by a sample-and-holdcircuit, i.e. only half of the total samples are used in deriving theoutput audio signal. If the protection level is C, then only one inevery three samples is used in deriving the output audio signal, i.e.one in every three successive samples is held for three consecutivesample periods. If the protection level is D, then only samples whichoccur during a specified interval are used in producing the output audiosignal. For example, this operation could be performed when only aspecified part of the recorded audio signal is to be allowed (by thecopyright owner) to be reproduced. If the final protection level is E,then no audio output signal is produced.

[0078] A third method of audio signal reproduction protection will bedescribed referring to the rightmost column in FIG. 12. In this case,protection control is executed by effecting control of the number ofgradation levels provided by the audio data samples, in a similar mannerto that described hereinabove for the video data. Generally, a digitalaudio signal has 16 bits/sample. When the final protection level is A,then all of these 16 bits are utilized, i.e. there is no limitation ofaudibility. If the final protection level is B, then the number ofeffective bits/sample is reduced to 12 (i.e. the low-order 4 bits ofeach 16-bit sample are fixed at 0), causing a lowering of quality of thereproduced audio signal. If the protection level is C, the number ofeffective bits is further reduced to 8, if the final protection level isD then the number of effective bits/sample is reduced to 4, and if thefinal protection level is E, then no audio output signal is produced.

[0079] It can thus be understood that the invention enables preciselimitation of reproduction of a recorded audio signal together withlimitation of reproduction of the recorded video signal, in accordancewith a combination of medium protection data and apparatus protectiondata.

[0080]FIG. 13 shows an example of the internal configuration of theaudio reproduction control section 16 d of this embodiment. For thepurpose of description, it is assumed that each of the above-mentionedthree methods of protection control of the audio reproduction controlsection 16 d is utilized, although in practice only one of these couldbe utilized. The circuit consists of a digital low-pass filter 61 whichreceives the output data samples from the sub-band combining section 16c via an input line 60, a sample-and-hold circuit 62 which can becontrolled to hold and output each data sample for a specific interval,a gradation control section 63 which effects the aforementioned controlof low-order bits of each audio data sample, to thereby control thegradation levels which can be expressed by each sample, a memory 64 fortemporarily holding successive data samples, and a digital-to-analogconverter 65 for converting the digital audio data to an analog audiosignal. The gradation control section 63 is controlled by a protectioncontrol signal to provide varying degrees of gradation in accordancewith the final protection level that has been determined for the audiodata, by setting varying numbers of low-order bits of each 16-bit audiodata sample to a fixed value as described above.

[0081] As shown, the protection control signal can also be applied tocontrol the sample-and-hold circuit 62, to effect the above-describedmethod of reproduction protection control utilizing sample-and-holdprocessing of the audio data samples. Similarly, the protection controlsignal can be applied to control the LPF 61, to achieve reproductionprotection control by varying the bandwidth of the audio signal. It willbe clear that a simpler circuit configuration can be utilized that thatshown in FIG. 13, if only one of the above three methods of protectioncontrol is applied.

[0082] In each of the embodiments described above, there is a fixedrelationship pattern between combinations of the protection levels whichcan be expressed by the medium protection data and the protection levelswhich can be expressed by the apparatus protection data, and therespective final protection levels which are thereby obtained, i.e. therelationship pattern which is stored in the matrix ROM of the finalprotection level determining section 13, an example of which is shown inFIG. 2. However in some cases there may be a requirement for enablingsuch a relationship pattern to be selected from a number of differentrelationship patterns, which have varying degrees of protectionseverity. Specifically, it may be advantageous to provide thereproduction apparatus with a switch which can be operated by the personwho is in charge of the reproduction apparatus, such that the switch canbe used to select from a plurality of different relationship patterns,so that the degree of reproduction protection can be flexibly determinedby that person. In that way, the person in charge of the reproductionapparatus can ensure that the reproduction protection will beappropriate for the viewing audience. For example, an adult can set theswitch such as to ensure that unsuitable scenes cannot be viewed by anychildren who may use the reproduction apparatus. In that case, assumingfor example that the relationship pattern which is the least severe isthat shown in FIG. 2, the entire range of possible relationship patternsis illustrated in the table of FIG. 14. Here, for each combination ofprotection levels obtained from the medium protection data and apparatusprotection data, there is a corresponding range of one or more possiblevalues of final protection level, with that range extending from a leastsevere value to the most severe value (i.e. protection level E). Onemethod of implementing such a capability would be to provide a pluralityof matrix ROMs (or to define a plurality of separate matrix regions in aROM), for storing the respectively different relationship patterns.However an embodiment of the invention will now be described wherebysuch a capability can be easily implemented by a simple modification ofany of the embodiments of the invention that have been previouslydescribed.

[0083] The embodiment, which is a modification of the embodiment of FIG.5, is shown in FIG. 15. The embodiment differs from that of FIG. 5 inbeing provided with a severity modification circuit 30 and a severitymodification setting switch 31. The severity modification circuit 30 isconnected between the final protection level determining section 13 andthe protection control signal generating section 14 a, and functions toselectively modify each protection level value which is read out fromthe matrix ROM of the final protection level determining section 13 (asdescribed hereinabove for the embodiment of FIG. 5), and to supply aresultant modified final protection level to the protection controlsignal generating section 14 a. The severity modification setting switch31 can be adjusted by the person who is in charge of the CD player, toselect one of five possible switch conditions which will be designatedas P_(A) to P_(E), respectively. The severity modification settingswitch 31 is coupled to control the severity modification circuit 30such that the severity modification circuit 30 executes protection levelmodification in accordance with the specific position at which theswitch is set, as described in the following.

[0084] The relationships between the five possible values of the mediumprotection level (determined by the medium protection signal detectionsection 11 as described hereinabove) and the five positions P_(A) toP_(E) of the severity modification setting switch 31, are shown for eachof the four possible values of the apparatus protection level(determined by the apparatus protection signal generating section 12),in diagrams (A) to (D) in FIG. 16. Referring first to diagram (A), ifthe switch position is P_(A), then the relationship between the mediumprotection level values, the apparatus protection level values and thefinal protection level values is left unchanged from those of thecorresponding column in FIG. 2, i.e. this setting of the severitymodification setting switch 31 provides the least severe degree ofreproduction protection. If the switch position is set to P_(B), thenthe least severe value which can be taken by the modified finalprotection level becomes level B. That is to say, if a protection levelA is established by the final protection level determining section 13,that is changed by the severity modification circuit 30 to a modifiedfinal protection level B. If the switch position is P_(C), then theleast severe value of the modified final protection level is changed toC. If the switch position is P_(D), then the least severe value of themodified final protection level is changed to D, and if the switchposition is P_(E), then the modified final protection level is fixed asE.

[0085] The same is true for each of the apparatus protection levelvalues 2, 3 and 4, as illustrated in diagrams (B), (C) and (D) in FIG.16, which correspond to the second, third and fourth columns in FIG. 2respectively.

[0086] It will be apparent that the severity modification circuit 30 canbe easily configured using a logic circuit, which implements a simplealgorithm in accordance with the setting of the severity modificationsetting switch 31, i.e. the algorithm would begin:

[0087] [If the severity modification switch 31 is set at P_(A), transferthe protection level value established by the final protection leveldetermining section 13 directly to the protection control signalgenerating section 14 a, as the final protection level.

[0088] If the severity modification switch 31 is set at P_(B), and ifthe protection level value established by the final protection leveldetermining section 13 is level A, change that to level B and transferto the protection control signal generating section 14 a as the(modified) final protection level. Otherwise, transfer the protectionlevel value produced from the final protection level determining section13 unchanged, as the final protection level.

[0089] If the severity modification switch 31 is set at P_(C), and ifthe protection level established by the final protection leveldetermining section 13 is level A or level B, change to level C, andtransfer to the protection control signal generating section 14 a as thefinal protection level. Otherwise, transfer the protection levelestablished by the final protection level determining section 13unchanged, as the final protection level . . . ], and so on.

[0090] Thus with this embodiment, if the severity modification settingswitch 31 is set to its least severe position (P_(A)), then therelationship pattern between combinations of the medium protection leveland reproduction apparatus protection level values will be as shown inFIG. 2. If the severity modification setting switch 31 is set to themost severe position (P_(E)), then the relationship pattern will be suchthat the final protection level will always be the highest level, i.e.level E. As the severity modification setting switch 31 is successivelychanged from positions P_(A) to P_(E), the least severe degree ofreproduction restriction (within the range of possible degrees ofrestriction which can be set by the final protection level) is increasedto a more severe degree, by successive steps.

[0091] For example if the apparatus protection level is 2 and the mediumprotection level is 4, then the final protection level will be B.However by altering the setting of the severity modification settingswitch 31, the user can change the final protection level to a highervalue, in the range B to E. Hence with this embodiment, althoughprotection level values can be specified by the manufacturer orcopyright owner of the recording medium, and by the manufacturer orseller of the reproduction apparatus, the final degree of protection canbe determined by the person who is in charge of the reproductionapparatus. Such a feature is highly useful.

[0092] As can be understood from the above description of embodiments,the invention enables a final protection level to be established, forcontrolling reproduction of recorded or transmitted video or audiosignals, with that final protection level being determined based on acombination of protection levels which are respectively separatelyestablished by the manufacturer or copyright owner of recorded signals(or broadcaster of transmitted signals, or copyright owner oftransmitted signal) and by the manufacturer or seller of thereproduction apparatus. The final protection level can be applied suchas to achieve extremely precise protection of reproduction, whereby forexample specific frames of a video signal, and/or specific regionswithin a frame, can be protected by restricting reproduction, with thedegree of restriction being variable in a stepwise manner. The inventioncan at the same time provide corresponding protection of an audio signalwhich is being reproduced in conjunction with a video signal.

[0093] Although the invention has been described in the above withreference to a CD player apparatus, it will be understood that theinvention is not limited in any way to such an apparatus, and is ingeneral applicable to reproduction protection in any type of apparatuswhich reproduces a recorded or transmitted video and/or audio signal.

What is claimed is:
 1. A reproduction protection method comprising:attaching medium protection data, which are specific to a data medium,to main data which represent an original signal, and conveying saidmedium protection data and main data by said data medium; supplying saidmain data and medium protection data via said data medium to areproduction apparatus; generating apparatus protection data which arespecific to said reproduction apparatus, within said reproductionapparatus; determining a protection level by combining the mediumprotection data and the apparatus protection data; and controlling saidreproduction apparatus to utilize said main data to reproduce saidoriginal signal in accordance with said protection level.
 2. Areproduction apparatus providing reproduction protection, for operatingon main data which are conveyed by a data medium and represent anoriginal signal and on medium protection data which are specific to saiddata medium and are conveyed by said data medium, the apparatuscomprising: means for generating apparatus protection data which arespecific to said reproduction apparatus; means for defining a protectionlevel based on said medium protection data and apparatus protection datain combination; and means for executing reproduction of said originalsignal by utilizing said main data, including means for selectivelyrestricting said reproduction in accordance with said protection level.3. A reproduction apparatus providing reproduction protection, foroperating on main data which are conveyed by a data medium and representan original signal and on medium protection data which are specific tosaid data medium and are conveyed by said data medium, the apparatuscomprising: means (10, 11) for detecting said medium protection data toobtain a medium protection signal expressing said medium protectionlevel; means (12) for generating an apparatus protection signalexpressing an apparatus protection level which has been assigned to saidreproduction apparatus; means (13) responsive to said medium protectionsignal and apparatus protection signal for determining a finalprotection level in accordance with a combination of said mediumprotection level and apparatus protection level, and generating a finalprotection level signal expressing said final protection level; means(15) for utilizing said main data to execute reproduction of saidoriginal signal, including means (14) responsive to said finalprotection level signal for selectively restricting said reproduction inaccordance with said final protection level.
 4. A reproduction apparatusaccording to claim 3 , wherein said main data are conveyed by said datamedium after having been compressed and encoded, wherein saidreproduction apparatus includes means (15 a, 15 b, 15 c) for decodingand means for decompressing said main data, and wherein said means forselectively restricting reproduction of the original signal comprisemeans for controlling at least one of said decoding means and saiddecompressing means in accordance with said final protection level.
 5. Areproduction apparatus according to claim 3 , wherein said main datacomprise video data which are conveyed by said data medium after havingbeen compressed by applying a transform operation upon each offixed-size blocks of pixel values within each frame of a video signal,wherein said decompressing means includes means (15 c) for applying aninverse transform operation, and wherein said means for selectivelyrestricting reproduction of the original signal serves to selectivelyeliminate specific ones of a plurality of transform coefficientsutilized in executing said inverse transform operation.
 6. Areproduction apparatus according to claim 3 , wherein said main data areconveyed by said data medium after having been compressed, quantized andencoded, wherein said reproduction apparatus includes means (15 b) fordequantizing said main data, and wherein said means for selectivelyrestricting reproduction of the original signal comprise means forcontrolling said dequantizing means in accordance with said finalprotection level.
 7. A reproduction apparatus according to claim 3 ,wherein said means for selectively restricting reproduction of theoriginal signal comprise means (52, 62) for periodically omittingselected portions of said main data from use by said reproductioncontrol means in reproducing said original signal.
 8. A reproductionapparatus according to claim 7 , wherein each of said selected portionscomprises at least one digital data sample.
 9. A reproduction apparatusaccording to claim 7 , wherein said main data express a digital videosignal, and wherein each of said selected portions comprises at leastone video signal frame.
 10. A reproduction apparatus according to claim3 , wherein said means for selectively restricting reproduction of theoriginal signal comprises gradation control means (51, 63) forselectively varying a number of signal amplitude gradations which can beexpressed by each data sample of said main data.
 11. A reproductionapparatus according to claim 3 , wherein said means for selectivelyrestricting reproduction of the original signal comprises controllabledigital low-pass filter means (61) for filtering said main data, tothereby controllably vary a bandwidth of a reproduced original signalobtained from said apparatus.
 12. A reproduction apparatus according toclaim 3 , wherein said medium protection data specify a mediumprotection level and protection position information, and wherein saidprotection position information specifies a portion of said main datawhich is to subjected to reproduction restriction in accordance withsaid final protection level.
 13. A reproduction apparatus according toclaim 12 , wherein said main data comprise a digital video signal, andwherein said protection position information specifies at least oneregion within each of a plurality of frames of said video signal.
 14. Areproduction apparatus according to claim 3 , further comprisingprotection severity modification means, operable for modifying saidfinal protection level which is determined by said combination of mediumprotection data and apparatus protection data, to obtain a modifiedfinal protection level.
 15. A reproduction apparatus according to claim14 , wherein said severity modification means comprise a manuallyoperable switch (31) provided on said reproduction apparatus, andseverity modification circuit means (30) coupled to said switch andcoupled to receive a signal representing said final protection level,for modifying said final protection level in accordance with a settingposition of said switch and thereby producing an output signalexpressing a modified final protection level.
 16. A reproductionapparatus according to claim 15 , wherein said final protection levelhas a value which defines one of a plurality of successively increasingdegrees of restriction of reproduction of said original signal,extending between a minimum and a maximum degree of restrictions andwherein said severity modification means is responsive to a change insaid setting position of the switch for changing only said minimumdegree of restriction.
 17. A data medium for transferring main datarepresenting an original signal to a reproduction apparatus, toreproduce said original signal by said reproduction apparatus, whereinsaid data medium further transfers medium protection data which arespecific to said data medium and wherein said reproduction apparatusgenerates apparatus protection data which are specific to saidreproduction apparatus, said medium protection data and apparatusprotection data in combination specifying a degree of restriction onsaid reproduction of the original signal by said reproduction apparatus.